Semaphorin 4D (SEMA4D), also known as CD100, is a transmembrane protein (e.g., SEQ ID NO: 1 (human); SEQ ID NO: 2 (murine)) that belongs to the semaphorin gene family. SEMA4D is expressed on the cell surface as a homodimer, but upon cell activation SEMA4D can be released from the cell surface via proteolytic cleavage to generate sSEMA4D, a soluble form of the protein, which is also biologically active. See Suzuki et al., Nature Rev. Immunol. 3:159-167 (2003); Kikutani et al., Nature Immunol. 9:17-23 (2008).
SEMA4D was first identified by generating two mouse monoclonal antibodies, BD16 and BB18, against activated human T cell clones (Herold et al., Int. Immunol. 7:1-8 (1994)). SEMA4D was the first example of a semaphorin expressed in the immune system. SEMA4D is expressed abundantly on the surface of resting T cells, and weakly on resting B cells, monocytes, and professional antigen-presenting cells, such as dendritic cells (DCs). Cellular activation can stimulate up-regulation of surface expression of SEMA4D on B cells and DCs, as well as the generation of sSEMA4D. SEMA4D is thought to function as both a receptor, which signals through its cytoplasmic domain, and as a ligand (Hall et al., PNAS 93:11780-11785 (1996)). One of the receptors identified for SEMA4D is Plexin-B1. Plexin-B1 is expressed in non-lymphoid tissues and is a high affinity (1 nM) receptor for SEMA4D (Tamagnone et al., Cell 99:71-80 (1999)).
SEMA4D is an important mediator of T cell and B cell activation. SEMA4D knockout (SEMA4D−/−) mice have reduced antibody responses to T-dependent antigens and impaired T cell priming. Both of these functions are restored upon the administration of sSEMA4D (Shi et al., Immunity 13:633-642 (2000)).
In addition to the demonstrated effects of SEMA4D on immune cells, SEMA4D also appears to play a direct role in the demyelination and axonal degeneration seen in neuroinflammatory diseases. The pathogenesis of inflammatory demyelinating diseases, such as MS, includes both an inflammatory phase involving immune cells as well as phases of selective demyelination and neurodegeneration. SEMA4D is expressed in central nervous system (CNS) oligodendrocytes and is an inhibitor of axonal regeneration. SEMA4D expression is up-regulated in oligodendrocytes at the periphery of spinal cord lesions (Moreau-Fauvarque et al., J. Neuroscience 23:9229-9239 (2003)). Culturing chronically activated T cells expressing sSEMA4D with human multipotent neural precursors or primary oligodendrocytes from rat brain induces apoptosis and process extension collapse (Giraudon et al., J. Immunol. 172:1246-1255 (2004); Giraudon et al., NeuroMolecular Med. 7:207-216 (2005)). SEMA4D induced apoptosis of neural precursors can be inhibited by the BD16 anti-SEMA4D antibody.
SEMA4D is also a potent pro-angiogenic molecule. Activation of Plexin-B1 through SEMA4D binding transactivates c-Met and promotes the invasive ability of tumor cells and promotes angiogenesis both in vitro and in vivo. Immunohistochemical analysis of SEMA4D in a large tumor sample collection revealed that SEMA4D overexpression is a very frequent event in head and neck, prostate, colon, breast, and lung cancers.
SEMA4D/Plexin-B1 signaling has also been shown to induce migration of endothelial cells and to promote migration of tumor cells (Conrotto et al., Blood 105:4321-4329 (2005); Giordano et al., Nature Cell Biology 4:720-724 (2002)). SEMA4D induced endothelial cell migration is prevented by SEMA4D-blocking antibodies and by SEMA4D knockdown. Knocking down SEMA4D expression in head and neck squamous cell carcioma (HNSCC) cells with SEMA4D short hairpin RNA (shRNA) before grafting into nude mice caused a dramatic reduction in tumor vascularity and tumor growth (Basile et al., PNAS 103:9017-9022 (2006)). Reports have recently pointed to a close correlation between inflammatory infiltration of the tumor stroma and a high vascular grade. SEMA4D is produced by inflammatory cells present in the tumor microenvironment. In an environment lacking SEMA4D, the ability of mouse breast cancer cells to originate tumor masses and metastases was severely impaired, and the source of SEMA4D was tumor associated macrophages (Sierra et al., JEM 205:1673-1685 (2008)).
Thus, there is a further need in the art for SEMA4D neutralizing molecules, e.g., anti-SEMA4D antibodies, for the treatment of cancers and neuroinflammatory diseases.